1. Field of the Invention
This invention pertains to a control system for a supercharged engine equipped with an automatic transmission and, more particularly, to a control system for controlling at least a primary supercharger which supercharges the engine in a low air intake rate region of operation and a secondary supercharger which supercharges the engine in a high air intake rate region of operation, as well as an automatic transmission.
2. Description of Related Art
Conventionally, some internal combustion engines for vehicles have at least a primary supercharger which supercharges the engine in a low air intake rate region of operation and a secondary supercharger which supercharges the engine in a high air intake rate region of operation. In such an internal combustion engine, these primary and secondary superchargers are selectively activated and sequentially controlled in accordance with previously provided, particularly designed switching patterns for various intake conditions of the internal combustion engine. Moreover, it is typical in such a control system to correct or change the switching patterns in accordance with the selected gears of the transmission in order to maintain a high supercharging condition.
In such a supercharged engine, which is equipped with an automatic transmission, as well as with first and second, or primary and secondary, superchargers, torque shock is produced upon switching the primary and secondary superchargers. Although such torque shock can be suppressed by precisely controlling the switching of the primary and secondary superchargers, it can not be avoided completely. Also, an automatic transmission is typically controlled so as to select a desired gear position in accordance with previously provided, particularly designed gear shift patterns for particular vehicle running conditions, or vehicle speeds, and engine operating conditions. Although gear shifting is precisely managed in order for the automatic transmission to eliminate gear shift shocks, since the operating condition of the engine changes during gear shifting, unnecessary switching of the primary and secondary superchargers may possibly occur in accordance with the switching patterns. In such a case, because the switching pattern is corrected according to gear shift positions, and the speed of the engine is increasingly or decreasingly changed during gear shifting, irregular switching of the primary and secondary superchargers is caused several times in a short period of time. For this reason, there is a chance that torque shock accompanying switching of the superchargers will be produced.